Effects of one valence proton on seniority and angular momentum of neutrons in neutron-rich $^{122-131}$Sb$_{51}$ isotopes

Abstract

Background: Levels fulfilling seniority scheme and relevant isomers are commonly observed features in semi-magic nuclei, for example in Sn isotopes (Z = 50). Seniority isomers in Sn, with dominantly pure neutron configurations, directly probe the underlying neutron-neutron (νν) interaction. Further, an addition of a valence proton particle or hole, through neutron-proton (νπ) interaction, affects the neutron seniority as well as the angular momentum.Purpose: Benchmark the reproducibility of the experimental observables, like the excitation energies (EX ) and the reduced electric quadrupole transition probabilities (B(E2)), with the results obtained from shell model interactions for neutron-rich Sn and Sb isotopes with N < 82. Study the sensitivity of the aforementioned experimental observables to the model interaction components. Further, explore from a microscopic point of view the structural similarity between the isomers in Sn and Sb, and thus the importance of the valence proton.Methods: The neutron-rich 122−131 Sb isotopes were produced as fission fragments in the reaction 9 Be( 238 U, f) with 6.2 MeV/u beam energy. An unique setup, consisting of AGATA, VAMOS++ and EXOGAM detectors, was used which enabled the prompt-delayed gamma-ray (γ) spectroscopy of fission fragments in the time range of 100 ns -200 µs.Results: New isomers, prompt and delayed transitions were established in the even-A 122−130 Sb isotopes. In the odd-A 123−131 Sb isotopes, new prompt and delayed γ-ray transitions were identified, in addition to the confirmation of the previously known isomers. The half-lives of the isomeric states